I have a friend with a 2011 F-450 with a Classy Chassis hauler bed (real nice BTW).
The bed adds about 1000 pounds over stock bed weight.
He has Firestone airbags.

He is a traveler, so the truck is packed with the essentials.
With his trailer hitched up and I'm guessing 3500+ of pin weight, the truck still has the sag, even with 55-60 PSI of air in the bags.

Anyone else experience this?

The Firestone airbags are rated to 100 psi. Has he tried more pressure? 55 psi in my bags will sit the truck the same height as empty with with 3100-3200 lbs of pin weight. My advice would be to take the bags up to 75-80 psi and see what happens.

Something just doesn't seem right in this situation. Either the weight of the body and the pin weight is more than he thinks it is, the truck springs are weak or a combination of the two. It sounds like he is dealing with 1200-1400 lbs more weight than me, but he is a 450 and I'm SRW 350. Did the upfitter than installed the body remove the helper springs or modify the stops that engage them?